FIGS. 1a-1d show a conventional apparatus 100 for conveying a glass tube strand or glass rod strand 101 having a circular cross-section. A plurality of support and guide members 103 made of graphite are disposed one after the other, if viewed in the direction of movement of the glass tube strand or glass rod strand 101, on a base plate 102, which may e.g. also be embodied as a machine frame. According to the sectional view of FIG. 1c and the perspective view of FIG. 1e, a V-shaped notch 104 may be provided on the upper side of the support and guide members 103. The moving glass tube strand or glass rod strand 101 is directly supported at the bottom of the V-shaped notch 104, and is guided in this manner.
For reducing the curvature of the glass tube strand or glass rod strand 101, i.e. the deviation of the glass tube strand or glass rod strand 101 from a straight line in the direction of movement of the glass tube strand or glass rod strand 101, it is conveyed such that it rotates continuously about its longitudinal axis. This can be accomplished for example by means of two pulling chains, which are covered with plates that engage the outer circumference of the glass tube strand or glass rod strand 101 and thus take it with them. If these pulling chains are not adjusted exactly in parallel with each other, a uniform rotation of the glass tube strand or glass rod strand 101 can be achieved during the conveyance along the drawing path.
Furthermore, one or more gas burners may be arranged along the drawing path, which heat the moving glass tube strand or glass rod strand 101 up to temperatures about the transition temperature of the respective type of glass used in order to further enhance the curvature of the glass tube strand or glass rod strand 101. For this purpose relatively large and wide gas burners are used that conventionally heat the entire cross-section of the glass tube.
This approach does not always enable a desired reduction in curvature of glass tube strands or glass rod strands. In particular, this approach is not suitable for conveying glass tube strands or glass rod strands having a cross-section that is different from a circular cross-section, in particular having an oval cross-section. Thus, there is need for further improvements.